1. Field of the Invention
The subject invention pertains to the art of antennas and particularly to a combination of elements which includes a phase array antenna enclosed within a dielectric lens, the combination of which is an antenna capable of providing scanned beams with hemispherical coverage.
2. Description of the Prior Art
Prior to the availability of high power microwave sources many of the antennas designed for radar systems were of the array type that operated at VHF and UHF frequencies. With the advent of the magnetron, however, interest in the array antennas waned and antenna designers concentrated their efforts on reflector and lens type antennas. These antenna types were easier to design, simpler to manufacture, were reliable and performed adequately in the target environment of the radar systems for which they were designed. These environments generally included relatively slow moving targets, one of which could be selected for tracking by the radar system. Modern radar systems, however, have been required to track a plurality of rapidly moving airborne targets over a wide range of vertical and horizontal angles. For example, applications exist wherefore hemispherical coverage and tracking capability is required. These requirements dictate specifications upon the antenna design that for many of the modern radar applications cannot be met by the mechanically rotating reflector and lens type antennas. Thus interest has been refocussed on phase array antennas because of their flexibility and rapid beam positioning capabilities. An antenna with rapid beam positioning characteristics and capable of providing the aforementioned hemispherical coverage is disclosed in U.S. Pat. No. 3,755,815, issued to John J. Stangel et al. on Aug. 28, 1973 and assigned to the assignee of the present invention. Hemispherical coverage is provided by the Stangel et al antenna with the utilization of a single phase array enclosed within a refracting surface which includes a plurality of modules, each comprising an element for receiving signals emitted from the array, a discrete element phase shifter for imparting phase shift to the received signals, and a transmitting element for radiating the phase shifted signal. Discrete elements for providing the refracting surface become impractical at frequencies above 10 GHz where they are lossy, subject to severe tolerance requirements, and are relatively expensive.
The subject invention discloses a dome constructed of dielectric material for imparting the required refraction to signals incident from the phase array to provide hemispherical coverage. This dome is relatively inexpensive and is not subject to severe tolerance requirements at the higher frequencies.